This invention relates to a control device of a hybrid vehicle which comprises an internal combustion engine as a source of power for running a vehicle and an electric motor having a high voltage battery as a power supply, the electric motor being used as a generator when the vehicle is decelerating and charged by the high voltage battery and a low voltage battery for vehicle-mounted electrical loads.
Recently, a hybrid vehicle has been developed comprising an internal combustion engine (gasoline engine) as a source of motive power for running a vehicle, and an electric motor having a high voltage battery as a power supply, as disclosed in Japanese patent publication Tokkai Hei 10-304511.
In this hybrid vehicle, the electric motor is used as a generator when the vehicle is decelerating (coasting) as a way of recovering the vehicle""s inertia energy while it is decelerating, and the power so generated is used to) charge the high voltage battery and low voltage battery for supplying vehicle-mounted electrical loads.
Control of the current when power is being generated by the electrical motor is based on the charge state of the high voltage battery, and the current supplied to electrical loads (vehicle-mounted electrical loads) such as auxiliary devices mounted on the vehicle. Specifically, a target charge current supplied to) the high voltage battery according to the charge state of the high voltage battery is computed, an electrical load current supplied to the vehicle-mounted electrical loads is detected, and the electric motor is controlled so that the sum of these values coincides with the current generated by the electrical motor.
During deceleration, if the generated current is too large when energy recovery is being performed, the high voltage battery will be overcharged. This leads to) early deterioration of the battery and excessive vehicle deceleration due to increase of the load on the electric motor; and consequently, the driver will experience an uncomfortable deceleration feeling.
If the high voltage battery is a lead-acid battery, which is used for its low cost in comparison to expensive lithium ion batteries or nickel-hydrogen batteries, it easily degenerates due to overcharging and it is especial necessary to prevent overcharging.
It is therefore an object of this invention to prevent overcharging of the battery, prevent deterioration of the battery due to overcharge% and to prevent the deceleration from becoming too large during energy recovery when the vehicle is decelerating
It is a further object of this invention to increase the enter recovery efficiency when the vehicle is decelerating. In order to achieve the above objects the invention provides a control device of a hybrid vehicle which provides an internal combustion engine as a power source for running a vehicle together with an electric motor. The control device comprises a high voltage battery which functions as a power source for the electric motor, a low voltage battery for vehicle-mounted electrical loads, a sensor for detecting a vehicle running state, and a microprocessor which controls the electric motor is programmed to determine a deceleration state of the vehicle, to cause the electric motor to function as a generator in the deceleration state, to perform control to charge the high voltage battery and low voltage battery by the current generated by the electric motor, and to limit the current generated by the electric motor by a limiter, and vary the value of this limiter according to the running state.
The details as well as other features and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.
FIG. 1 is a system diagram of a hybrid vehicle showing one embodiment of this invention.
FIG. 2 is a system diagram of a power supply system in the hybrid vehicle.
FIG. 3 is a control block diagram of generation current control of a motor-generator.
FIG. 4 is a flowchart of a control operation performed by a first limiter.
FIG. 5 is a flowchart showing a control operation performed by a second limiter.
FIG. 6 is a diagram showing a typical setting (1) of a limiter value of the second limiter.
FIG. 7 is a diagram showing a typical setting (2) of a limiter value of the second limiter.
FIG. 8 is a diagram showing a typical setting (3) of a limiter value of the second limiter.
FIG. 9 is a diagram showing a typical setting (4) of a limiter value of the second limiter.
FIG. 10 is a diagram showing a typical setting (5) of a limiter value of the second limiter.